INFIDELITY, self-harm and depression inside a seemingly fairytale marriage were the revelations that shocked the world.
Twenty years on from the death of Princess Diana, biographer Andrew Morton has published previously secret tapes of the young royal pouring her heart out for the book that became her "lifebelt against being drowned."
Now 60 Minutes will detail the equally dramatic "story behind the story" of how the tapes were clandestinely recorded in the palace without the royal family's knowledge.
Having interviewed Morton for Sunday night's feature, journalist Liz Hayes said she was struck by the young princess' "determination" to air her side of the toxic marriage and the desperate situation she found herself in.
"It's just vaguely hysterical really that it did involve a friend riding his bicycle to the palace and having lunch and surreptitiously pinning a microphone to a recorder with a cassette in it. And he'd be armed with a list of questions from Morton," she told news.com.au.
"It is quite amazing the lengths they had to go to get Diana to be able to say in first person what her situation was and tell her story. But at the same time they had to agree to never let on it was her and it wasn't until she died really that they were in a position to say that it was her."
At the time of publication in 1992, Morton's book, Diana, Her True Story In Her Own Words, scandalised the UK after an extract published a newspaper told she was "driven to five suicide bids" by Charles.
It was banned in books and supermarkets and led to calls from one MP for Morton to be locked up in the Tower of London for treason. Hayes said it was deemed "sacrilegious" and "nobody wanted to believe it".
"Ironically, a biography written and produced with Diana's enthusiastic co-operation was being piously boycotted on the suspicion it was a pack of lies," Morton recently wrote about the furore.
'SH*T SCARED' ROYAL
The controversial book came about due to Morton's friendship with Dr James Colthurst, who had known Diana since they were teens and knew about her bulimia and unhappiness over Charles's affair.
Feeling trapped between the stony-faced royal family and a lifetime of unhappiness, Morton said Diana began leaking him information via Colthurst he would publish as articles. She eventually agreed to "interviews by proxy" in the palace on Morton's behalf that involved hiding the microphone under cushions if someone knocked on the door. She also smuggled him passionate notes between Charles and Camilla as "proof" of their infidelity and swept her living room for bugs in paranoia.
The tapes, which have been published as transcripts to mark 25 years since the book and 20 years since her death, reveal a sense of the princess in her own words. They cover her struggles with bulimia, depression, jealousy and being "sh*t scared" at public events, including the "make or break" Australian tour where Prime Minister Malcolm Fraser suggested she bring baby William.
They also reveal Charles' "jealously" at the public's growing preoccupation with the royal princess which she bore the brunt of.
"He took it out on me. He was jealous; I understood the jealousy but I couldn't explain that I didn't ask for it," she said.
Hayes said she's not surprised with the public fascination with Diana, two decades on from being tragically killed in a Paris car crash in August 1997.
"She was 36 when she died. That's incredibly young. She captured us from the moment she arrived, she's this innocent young girl who wins Charles' heart and I guess it started from there," she said.
"Her life unravelled in a manner that I don't think a lot of people would have trouble understanding because these are things I think a lot of people have trouble with in their own lives; infidelity, eating disorders, the self harm issues, … lots of people would related to that. She just seemed a mum who loved her boys."
The anniversary coincides with a year her sons, Prince William and Prince Harry, along with the Duchess of Cambridge, have spearheaded a mental health campaign by opening up about the effects of their mother's death for the first time. They also criticised the "stiff upper lip" culture in Britain that led them to shut down afterwards.
Hayes said she's in no doubt that the young royals, including the Duchess of Cambridge, have taken their lead from their mother's relaxed and natural approach.
"They know why Diana was adored and that is because she made herself very accessible and she's very happy to put herself among the people. Her sons and Kate understood that's a better way to operate rather than standing high above us all."
"Intentional or unintentional, I think it came from Diana anyway that they've learned to engage with people in a way that makes people very comfortable. And all power to them."
Diana's Secret Tapes will air on 60 Minutes Sunday 7:30pm on Channel Nine.